Bright, energy-efficient, and stable white lighting sources, such as light-emitting diodes, are desirable to mitigate climate change. A near-ultraviolet-excitable, green-emitting Ca2LaHf2Al3O12:Ce3+,Tb3+ garnet phosphor with high photoluminescence efficiency, prepared by solid-state synthesis, is described. X-ray diffraction Rietveld refinement reveals its garnet structure with space group Ia3d and crystallographic parameters a = b = c = 12.528 Å, α = β = γ = 90°, and V = 1966.470 Å3. On 408 nm excitation, it produces bright green light peaking at 543 nm owing to the 5D4→7F5 transition of Tb3+ ions and demonstrates an ultrahigh internal quantum efficiency (80%) and high external quantum efficiency (59.2%). The luminescence intensity of Ca2LaHf2Al3O12:0.05Ce3+,0.6Tb3+ is double that of a Ca2LaHf2Al3O12:0.05Ce3+ green phosphor owing to Ce3+→Tb3+ energy transfer. This Ca2LaHf2Al3O12:0.05Ce3+,0.6Tb3+ green phosphor was used to fabricate a near-UV-pumped white LED device; the resulting luminous efficacy and color rendering index at 3397 K were 17.56 lm/W and 93.1, respectively.